The artificial kidney has been accepted as a major advance in maintaining the lives of people suffering from irreversible kidney failure. It is also used as an interim support system for patients suitable for kidney transplantation. Hemodialysis is a successful long-term life support method so that the people requiring treatment increase each year at a rate approximately 35 per million population.
Existing forms of artificial kidneys that are used clinically demonstrate problems in many areas primarily in efficiency, compatibility with the patient, and cost of use. These types of problems are amenable to solution by engineering analysis and techniques. Collaboration between the Renal Unit of the Vancouver General Hospital and the Mechanical Engineering Department at The University of British Columbia in 1966 sponsored by both MRC and NRC grants resulted in a Ph.D. by H. R. Davis entitled "The Design of a Capillary Artificial Kidney", Ph.D. Thesis, The University of British Columbia, Canada, wherein a new concept for a hemodialyzer configuration was developed. This thesis stated a theory for mass transfer of impurities from blood to dialysate through a capillary membrane and optimized the transfer process. An important part of the thesis dealt with the fluid mechanics of the blood circuit in the dialyzer by a novel method of distributing blood from the feeder lines to the capillaries.
Construction of a number of prototype capillary artificial kidneys was commenced in order to provide experimental verification of the design given in the Ph.D. thesis. Tests were performed with physiological saline solutions, with blood from the hospital blood bank, and on dogs under simulated kidney disease conditions. The prototype kidneys were constructed with either cellulose or plastic capillaries as these were the only useful fibres that could be obtained for experimental use. Several months of testing under various conditions conclusively demonstrated that the prototype artificial kidney with plastic capillaries met the original design constraints and could achieve a level of operating efficiency and blood compatibility unmatched by any other existing system, as shown in the article by the present inventors Price, J. D. E., Davis, H. R., Parkinson, G. V., and Brockley, C. A.; "A New Capillary Hemodialyzer", Ann. Roy. Coll. Phy. and Surg. 6:1, p. 40, Jan., 1973.
Work has been conducted on the manifolds used to distribute blood from a single feeder line to many thousands of capillaries. The design of this new manifold configuration followed the criteria set out for the earlier manifold described in the thesis by David (supra). The object of this work was to achieve a design which would allow an artificial kidney containing more than 10,000 capillaries to have uniform blood distribution with only one arterial and venous manifold.
The successful design should maintain laminar blood flow everywhere in the manifold, distribute blood uniformly to every capillary, have no regions of stagnation where thrombus formation could occur, have a minimum internal volume to conserve the patients blood, and be non-traumatic towards blood. These conditions were met by forming a compound manifold. That is, a primary manifold (which used a linear area decrease cross-section in the downstream direction) fed fluid to a secondary manifold (also a linear area decrease cross-section) which fed fluid to the capillaries. An important element of the design is the provision of turning vanes between the primary and secondary manifold sections.
The design of a manifold for capillary artificial kidneys that meets the physiological requirements of blood transport while achieving uniform fluid distribution has been accomplished. Flow visualization showed that laminar fluid flow existed everywhere in the header and thus thrombus formation probably would not be accelerated. The physical shape of the manifold is convenient for construction purposes and achieves the goal of low internal blood volume. Experimental work with blood demonstrated that clotting in the headers and capillaries is not a problem, provided that non-thrombogenic materials are used.